It is customary to provide a row crop unit on a forage harvester when standing corn is to be processed into silage. The row crop unit may engage 1, 2 or more rows of corn. For each row of standing corn a cutting mechanism and a gathering and conveying mechanism is provided. Various types of conveying mechanisms have been employed, but the most widely accepted type embodies two side by side metal conveyer chains provided with lugs, the chains engaging crop material between adjacent rearwardly running runs. The chains may be provided with metal lugs, or, as shown in U.S. Pat. No. 3,339,354, resilient flexible lugs. When chains and lugs of conventional design are employed, it is necessary to provide upper and lower conveying chains as the crop material is not firmly engaged between the chains. However, when using chains provided with elements, such as shown in U.S. Pat. No. 3,339,354, it is only necessary to provide one pair of side by side conveyor chains for each row as the crop material is gripped between adjacent runs of the conveyor. A primary disadvantage of both of these forms of conveying mechanisms is that if one of the chains breaks, it in turn may enter into the cutting mechanism of the forage harvester causing severe damage to the knives, the knife supports, the shear bar, etc.. Additional disadvantages of these conveying mechanisms are high wear rates, noisy operation, high weight and relatively high cost.
In order to overcome the foregoing disadvantages, it has been proposed in U.S. Pat. Nos. 3,854,272 and 3,940,913 to utilize a gathering mechanism utilizing molded rubber belting of the type which is occasionally referred to as snowmobile belting. The molded belting has drive lugs on one side of the belt and crop engaging or gathering lugs on the other side.
Prior art designs which have utilized molded belting, while overcoming many of the disadvantages of chain type belts, have experienced other problems. The basic problem is that these belts tend to jump the driving or idler sprockets, or they tend to shift thereon causing damage to the drive and gathering lugs which will eventually result in failure of the belts. One of the reasons for these problems is that these belts have been utilized in prior art designs to drive a rotary cutting mechanism which severs the standing crop. Since the rotary cutting mechanism requires a fairly high torque, particularly when the cutting mechanism is not properly adjusted, the belt which drives the cutting mechanism tends to elongate to the point where it jumps off the sprockets or breaks. Also, the drive belt may be thrown from the sprockets if the cutting mechanism jams. A second reason for these problems arises from trash clearance. Thus, in prior art designs the trash tends to build-up on the cutting mechanism, the sprockets, and the supporting frame disposed below the belts, the accumulated trash causing the belts to jump the sprockets or to stretch to a point where they no longer perform in a satisfactory manner. Another reason for these problems is that prior art tensioning mechanisms fail to maintain proper tension of the belts.
Another disadvantage of prior art designs which utilize molded belting to drive a rotary cutting mechanism is that it is not possible to properly locate the forward ends of adjacent belts with respect to the cutting mechanism. Thus, when one of the belts is utilized to drive a rotary cutting mechanism it is not possible to properly gather and engage the crop material between adjacent rearwardly running sides of the cooperating gathering belts. It is desirable that crop material be firmly engaged before cutting, since if the material is not engaged between adjacent runs of the conveying mechanism the crop material may fall to the ground when it is cut and not enter into the harvester. In addition, with the prior art constructions, the belts cannot properly gather the crop material.